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Emergency braking in space

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Re: Emergency braking in space

#31

Post by Someone »

pavel_lishin wrote: post #4

I wonder what sort of spaceship would be capable of emergency deceleration at 4g for nine days, but would choose a leisurely 0.1g cruise to get up to .1c over the course of over a year instead. edit: actually, what sort of rotational rings would withstand that 4g load? Surely they'd break apart. I guess that might be part of the fun and exciting plot - the rush to move vital equipment into the core of the ship, and c…

If power requirements as a function of acceleration/deceleration rate are above linear, it might be more economical to accelerate slowly, especially.

Also, the faster acceleration/deceleration might be less comfortable, destroy cargo, wear out the engine faster, etc.

Re: Emergency braking in space

#32

Post by KineticLensman »

I think this illustrates how hard it is to write SF plots involving 'mundane' interstellar travel (no warp drives or wormholes) that make approximate sense in terms of the laws of physics but which also reflect the enormous energy required and the sheer complexity of the task. Going to a different star is nothing like going to the moon but with a much larger Apollo. Simple plot devices (there's something in the way that we didn't detect before launch and didn't otherwise consider) really don't stand up very well.

Re: Emergency braking in space

#33

Post by ghusbands »

ericbarrett wrote: post #18

I think it would be impossible for humans to walk around at more than ~1.5 g of acceleration for extended periods of time, and even that is asking a lot. Take the g-force and multiply it by your body weight. That would be how heavy you feel when standing. If you are 70 kg (154 lbs) and under 1.5g of acceleration that is an extra 35 kg (77 lbs) of weight, which is about what we ask a modern soldier to carry. But the s…

You could discount a lot of extra weight over time (physiological adaptation), especially as you're not carrying it in your arms or over your shoulders, but tripping up would suddenly become a lot more fatal. Everyone's reactions and instincts are tuned for 1g.

Re: Emergency braking in space

#34

Post by ghusbands »

Mister_Snuggles wrote: post #8
throwaway09223 wrote: post #7

If a ship is capable of continuous 1g acceleration then it shouldn't be designed with rotating centrifugal rings for gravity. Instead, design the ship with the floor towards the engine and travel at a constant 1g to wherever it is that you're going. Decelerate at the same speed.

I'm really surprised by this oversight as other things (magnetic boots) from The Expanse were explicitly mentioned. In The Expanse, this is exactly how ships are set up. The "floor" is towards the engine and the continuous 1g acceleration provides "gravity". When a ship starts decelerating there is a "flip and burn" where everyone straps in while the ship literally turns around and starts accelerating at 1g in the op…

It could just flip much more slowly and maintain ~1g, with minimal course correction.

Re: Emergency braking in space

#35

Post by KineticLensman »

hammock wrote: post #30
TremendousJudge wrote: post #28

Earlier quoted context omitted.

It's not the same though. When at higher gravity, you're not carrying more weight like a backpack or like extra fat -- your regular tissues weigh more. This includes your blood and other fluids, but your heart is still the same strength. I'd expect that to make a difference.

That’s a really interesting point. I wonder if there are “artificial exohearts” or something that we could install on the extremities to keep vital body fluids like blood and lymph flowing when the heart is not strong enough.

Then you have to toughen up the internal tissues so that blood vessels aren't ruptured by high-pressure blood (which can cause strokes, permanent vision loss if retinal arteries are affected, etc). High blood pressure also affects kidney and liver function, amongst other things.

Re: Emergency braking in space

#36

Post by tablespoon »

hammock wrote: post #30
TremendousJudge wrote: post #28

Earlier quoted context omitted.

It's not the same though. When at higher gravity, you're not carrying more weight like a backpack or like extra fat -- your regular tissues weigh more. This includes your blood and other fluids, but your heart is still the same strength. I'd expect that to make a difference.

That’s a really interesting point. I wonder if there are “artificial exohearts” or something that we could install on the extremities to keep vital body fluids like blood and lymph flowing when the heart is not strong enough.

> That’s a really interesting point. I wonder if there are “artificial exohearts” or something that we could install on the extremities to keep vital body fluids like blood and lymph flowing when the heart is not strong enough.

Isn't that basically a g-suit, like fighter pilots already wear?

https://en.wikipedia.org/wiki/G-suit

Also, from that page:

> The resting g-tolerance of a typical person is anywhere from 3–5 g depending on the person.

Re: Emergency braking in space

#38

Post by joncrocks »

ghusbands wrote: post #34
Mister_Snuggles wrote: post #8

Earlier quoted context omitted.

I'm really surprised by this oversight as other things (magnetic boots) from The Expanse were explicitly mentioned. In The Expanse, this is exactly how ships are set up. The "floor" is towards the engine and the continuous 1g acceleration provides "gravity". When a ship starts decelerating there is a "flip and burn" where everyone straps in while the ship literally turns around and starts accelerating at 1g in the op…

It could just flip much more slowly and maintain ~1g, with minimal course correction.

Presumably the mid-point is where the ship would be travelling at maximum velocity, so the course correction may not be as minimal depending on how slowly we're talking. It might be this would use more fuel/mass.

Re: Emergency braking in space

#40

Post by Johnny555 »

TremendousJudge wrote: post #28
ginko wrote: post #19

Earlier quoted context omitted.

>Go higher and it gets even less plausible. 2.0g is like carrying your twin. FWIW there are people who weigh well beyond 150kg so I'd argue it would be plausible. Will people be able to perform at peak physical level? No. Will they probably manage for a couple of days? I'd say so.

It's not the same though. When at higher gravity, you're not carrying more weight like a backpack or like extra fat -- your regular tissues weigh more. This includes your blood and other fluids, but your heart is still the same strength. I'd expect that to make a difference.

Wall-E found a solution this problem - people don't need to walk, they have mobile beds to move around.

https://www.youtube.com/watch?v=s-kdRdzxdZQ

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